The present invention relates to a switching controller in whose control loop an error signal amplifier is provided, which exhibits P (proportional) action and which acts on a pulse duration modulator or frequency modulator for the final controlling element of the switching controller.
A controller of the above-mentioned type is described in European Patent No. 0 355 333.
PCT Application WO 97/34363 describes a switching controller which, besides the conventional control loop for the error signal at the output of the switching controller, has an additional control loop with which a correction quantity, which is a function of the load variation, is computed. This correction quantity is additively superimposed on the error signal in order to reduce voltage fluctuations given pulse-shaped load variations at the output of the switching controller.
U.S. Pat. No. 4,885,674 describes a similar switching controller having two such control loops.
In the switching controller described in European Patent No. 0 355 333, noise signals on the input voltage are optimally suppressed in their effect on the output voltage of the switching controller without the control rate being adversely affected, for instance given sudden load variations. In order to prevent large voltage dips given sudden load variations at the output, for instance in the TDMA operation of a traveling-wave amplifier in a satellite, the voltage control loop must be properly dimensionally designed (high P component in the error signal amplifier). This can only be done when accompanied by a large enough output capacity, if the aim is for no stability problems to occur.
In accordance with the present invention, it is possible to dimensionally design the control loop to have a low P components. The output capacities of the switching controller can be reduced without causing control stability problems. This leads to a smaller type of construction for switching controllers in high-voltage parts, where substantial outlay is required for smoothing capacitors.
In accordance with the present invention, the control loop can be dimensionally designed to have a low P-component using so-called forward (unidirectional) control; circumventing the error signal amplifier. The step change in load is directly detected and delivered to the pulse-duration or pulse-frequency modulator, without the actual control loop having to respond. As a result of this precontrol, fewer automatic control delays follow step changes in load, without giving rise to stability problems.
When only the alternating component of the load current is detected for the precontrol, the precontrol decays with a time constant that can be selected such that the error signal amplifier can easily compensate for the decaying precontrol.